A problem associated with conventional soluble fertilizers such as urea is that the fertilizer particles become tacky when applied under high humidity conditions. Critical relative humidity values for a variety of fertilizer products has been compiled and shows that the application of fertilizer products at a critical relative humidity at 30° C. of above 40% causes the particles to become tacky [Manual for Determining the Physical Properties of Fertilizer, 2nd Edition, International Fertilizer Development Center, Muscle Shoals, Ala., February, 1993, pp. 5-7. Tackified fertilizer particles associated with a degree of hydration is known to cause phytotoxicity and the rapid depletion of nutrients from the particle through leaching. An additional handling problem associated with hygroscopic fertilizer particles is that the particular tends to mass into a cake that impedes in a form particle distribution onto soil.
Attempts to encapsulate a fertilizer particle in a coating to improve humidity stability have included sulfur coating as exemplified in U.S. Pat. No. 3,342,577; VOC solvated polymer resin spray, as exemplified in U.S. Pat. No. 3,475,154; epoxy resin cure on the particles surfaces, as exemplified in U.S. Pat. Nos. 3,264,088 and 3,259,482; and multiple layer coatings, as exemplified in U.S. Pat. No. 5,698,002.
While attempts to reduce the moisture sensitivity of fertilizer particles containing hygroscopic plant nutrients has proven somewhat successful, the use of such a coating is complicated when fertilizer particle surface is decorated with an active agent intended to inhibit target plant pests or weed growth. The inclusion of a surface active agent on hygroscopic fertilizer particle, the particle absorption of even a small amount of water that would otherwise not lead to fertilizer release associated with chemical burning, induces phytotoxicity associated with a chemical burn caused by active agent adhesion onto target plant foliage. In applying the active agent surface decorated fertilizer particle, a conventional formulation to turf under even moderate humidity conditions, results in undesired turf effects, such as a tire tracking, discoloration, and thinning, with these problems being compounded when the material is applied to closely mowed hybrid Bermudagrass, Bentgrass, Bluegrass, Fescue, St, Augustine, Ryegrass, or other grass, depending on the phytotoxic characteristic of the active agent.
Since studies have shown that the same concentration of herbicide granules applied directly to soil on non-tackified fertilizer particles do not induce chemical burns on the target foliage, there exists a need to preclude active agent granule, powder, or liquided active agent decorating hygroscopic fertilizer particle from becoming adhered to target foliage. There further exists a need for the development of an intermediate coating between the hygroscopic fertilizer particle and surface decorating active agent granule, powder, or liquid that performs dual functions of rendering hygroscopic fertilizer particle slower towards water absorption while simultaneously adhering active agent granules. While prior art hygroscopic fertilizer particle coatings have succeeded in providing the first attribute of this need, the second attribute has remained lacking.